The Creation of a Human-Monkey Chimera

Monkey-human blastocyst
It is not much to look at, but what you see above is a human-monkey chimera. Image taken from reference [5].

I am a little behind the times on this one. Apparently, back in April of this year, scientists successfully created the first human-monkey chimeras.[1] A chimera describes an organism that contains cells from different types of creatures. Note that a chimera is different from a hybrid. A hybrid is created by interbreeding two different species of animal. A mule is a hybrid of a donkey and a horse. Sperm from a donkey fertilizes the egg of a horse and the resulting embryo grows into a mule. In the creationist model, hybrids represent separate species that belong to the same kind: their genetics are compatible because they belong to the same, larger gene pool.

In contrast, a chimera is not created by interbreeding. Suppose a horse embryo were created and a donkey embryo were created and then these two embryos were blended together so that the cells of the horse embryo and the donkey embryo joined together forming a single embryo. This chimeric embryo would have some cells that are genetically horse cells and some cells that are genetically donkey cells. If the embryo is capable of developing and growing into a fully developed organism, the animal would have patches of tissue that are horse and other patches of tissue that are donkey. For example, the left eye might be a horse eye while the right eye is a donkey eye. The right foot might be a horse foot while the left leg might be a donkey leg. The animal would essentially be a patchwork of horse and donkey.

A sheep-goat chimera. Note the patch of wool on the animal’s lower shoulder. That is a patch of sheep skin on an animal that otherwise looks more like a goat. Image taken from reference [3].

By the way, when I say “blend the embryo of a horse and a donkey,” I do not mean stick two embryos with distinct heads, bodies, and limbs into a blender and hope things go okay. I am talking about the very early stages of an embryo, when the embryo is nothing more than a ball of featureless cells. Since there is no structure to the embryo at this early stage, cells can be added to, or taken away from, the embryo and there would still be enough information available for the embryo to develop.

Scientists have been able to produce chimeras for a while now. The first reported chimeras were of a sheep and a goat back in 1984.[2] While not all chimera embryos make it to birth, some do.[3] One of the main interests in creating chimeras is to study embryo development. In order for a chimera embryo to develop, the cells from the two different types of animals have to be able to communicate with one another. Such communication is needed to tell where the various cells are supposed to go and what structures they will create.

Now, before you begin to think that scientists have created some horrible monstrosity of a monkey-man, the human-monkey chimera only lasted 20 days. The embryos of crab-eating macaques were allowed to develop on their own until day six after fertilization. The embryo would be little more than a featureless ball of cells at this point. Then, 25 human stem cells were inserted into each monkey embryo.[4] The embryos were allowed to develop for 20 more days, after which, they were destroyed.[5] Note that the remaining chimera embryos were destroyed after 20 days: out of 132 embryos that were found to have human cells within them the day after the human cells were injected, only three survived until the 19th day.[6] 

Many of the articles that I found noted that such a human-monkey chimera raises ethical concerns. Interestingly, many of them did not describe what those concerns were, just that there were concerns. One specific concern that was mentioned was “the moral status of these novel creatures.”[7] I suppose that means, if human cells and monkey cells can create a single organism, is the organism a monkey, or is it a human? Does it have some rights, given its human “parentage,” or is it merely an animal to be experimented upon (or to be used as an organ donor)?

I will circle back around to the question of what are these chimera embryos. First, I want to address a few other things. First of all, the immediate moral concern I had was, where are the human stem cells coming from?

Stem cells are cells that are capable of developing into other types of cells. In your body, you have hundreds of types of cells, each with a special function and purpose. If the early embryo begins with generic cells with no structure or function, where do all of these specialized cells come from? From stem cells, cells whose whole function is to produce new cells, and then these new cells can become specialized for particular functions.

The most obvious source of stem cells are from an embryo. An early embryo is pretty much made up entirely of stem cells. These stem cells are sometimes called totipotent stem cells, because they are capable of developing into any type of cell in the body. Embryonic stem cells are easily the most controversial stem cells because in order to harvest these stem cells, the embryo has to be destroyed. If you believe that life begins at conception, then harvesting embryonic stem cells is the murder of unborn children in order to use their cells in experiments.

However, there are other types of stem cells in addition to embryonic stem cells. A common example are the stem cells found in red bone marrow. These stem cells are found in any human, even an adult. As they grow and develop, these stem cells can became any type of blood cell found in the body (red blood cells, white blood cells, T cells, B cells, and megakaryocytes, which produce platelets). These are not totipotent, since they cannot produce any type of cells. Even though they are limited to the production of blood cells, it is possible to take these stem cells and stimulate them to produce other types of cells, such as skin or muscle. These cells are sometimes called pluripotent stem cells, because they can be used to produce a wide variety of cells.

Now, as best as I can tell, the human stem cells used in the study were pluriopotent stem cells, not totipotent stem cells. I have not been able to access the full research article, but the summary specifically mentions using human pluripotent stem cells[8] and another article mentioned that the human cells were derived from mature skin or blood cells that were reprogrammed.[9] Therefore, it looks very certain that embryonic stem cells were not used in this study. As far as the morality of using cells from destroyed embryos goes, the researchers’ hands appear to be clean.

The second thing I want to address is the supposed significance of this study. Believe it or not, this is not the first time human-animal chimeras have been created.[10] Thus, it has already been shown that human-animal chimeras can be created. What makes this particular study “so special” is that it is a chimera between a human and a “close relative,” a monkey.[11] Thus, this research is especially significant to an evolutionist who believes that humans and monkeys show a more recent common ancestor than they do with, say, a pig or a rat.

The significance of putting human stem cells in the embryo of a “close relative” is that it is expected that such a chimera would be more likely to develop and more easily accept the human stem cells, thus making a more effective chimera. Since one of the goals of creating human-animal chimeras is to create a source of organ donors,[12] creating effective chimeras would be a terrific boon.

However, as a creationist, humans are separated from animals as a distinct type of creation. Sure, our bodies share many characteristics with animals, specifically mammals and primates. However, we still belong to separate kinds, so there is no necessary reason to think that human cells can effectively communicate with monkey cells. Perhaps they can: the human-monkey chimeras seemed to accept the human cells rather well,[13] but whether or not these chimeras could be brought to term is another question altogether. Then the actual effectiveness of transplants from these chimeras to humans would have to be tested. After all, these chimeric embryos were only allowed to last twenty days: we have no idea what would happen to them after that. I predict that, because they belong to separate kinds, such chimeras would probably fail in the long run.

What does that leave us with? What should be consider these embryos to be? I think that the answer is quite simple: they are monkey embryos with human cells. Consider an analogous example. Suppose a monkey were to have human skin grafts added to it. The human skin grafts contain human cells, such such a monkey would technically contain human cells within its body. Would we call a monkey with human skin grafts a monkey, a human, or some other kinds of novel creature? No, we would probably call it a monkey with human skin grafts. In a similar manner, these chimeric embryos are not some sort of new creature, they are monkey embryos with human cells added. Sure, the human cells may be incorporated into the embryo at a more fundamental level than the monkey with skin grafts, but it is still just a monkey with human cells added. Remember, the human cells added were derived from an adult human, not from an embryo. The embryonic development began with a monkey and, in more opinion, it remains a monkey, even if human cells are “grafted” in.

My conclusion is that these scientists have not done anything morally wrong, in the sense that I do not believe that they have violated any of God’s moral laws. However, I think they are guilty of a type of hubris. They believe that, as the products of evolution, they are capable of creating novel creatures for their own benefit and experiment. Living things are just another things to be played with an tooled around with, since they are just the product of evolution anyway. They are playing God, or perhaps I should say that they are playing Darwin. It is that mentality, that humans are a thing to be experimented with, that I dislike, more than what they actually did.By the way, the scientists knew they were walking a fine line between what was ethical and what was not. They did, after all, use pluripotent stem cells rather than embryonic stem cells. They destroyed the embryos after twenty days in order to not have to deal with the issue of a fully developed monkey-human monstrosity. However, they also conducted their experiments in China.[14] While it was not stated in anything that I read, my guess is that it is a lot easier to do something ethically dubious in China that it is in the United States. They knew they were pushing the boundaries of what was acceptable. But can we accuse them of violating any specific moral law? I do not think so.

Thoughts from Steven

[1]Hotz, Robert Lee (2021) “Creation of First Human-Monkey Embryos Sparks Concern” The Wall Street Journal retrieved from on June 25, 2021

[2]Fehilly, Carole; S. M. Willadsen; Elizabeth Tucker (1984) “Interspecific chimaerism between sheep and goat” Nature 307(5952): 634-636

[3]Ruffing, N. A.; G. B. Anderson; R. H. Bondurant; W. B. Currie; R. L. Pashen (1993) “Effects of Chimerism in Sheep-Goat Concepti That Developed from Blastomere-Aggregation Embryos” Biology of Reproduction 48: 889-904

[4]Cell Press (2021) “Researchers generate human-monkey chimeric embryos” Phys.Org retrieved from on June 26, 2021

[5]New Scientist and Press Association (2021) “Human cells grown in monkey embryos raise ethical concerns” NewScientist retrieved from on June 26, 2021

[6]Cell Press (2021) “Researchers generate human-monkey chimeric embryos” Phys.Org retrieved from on June 26, 2021

[7]New Scientist and Press Association (2021) “Human cells grown in monkey embryos raise ethical concerns” NewScientist retrieved from on June 26, 2021

[8]Tan, Tao; Jun Wu; Chenyang Si; Weizhi Ji; Yuyu Niu; Juan Carlos Izpisua Belmonte (2021) “Chimeric contribution of human extended pluripotent stem cells to monkey embryos ex vivoCell 184(8): P2020-2032 retrieved from on June 26, 2021

[9]Hotz, Robert Lee (2021) “Creation of First Human-Monkey Embryos Sparks Concern” The Wall Street Journal retrieved from on June 25, 2021



[12]In theory, since they contain human cells, the organs are compatible with human and thus make good transplants. Since they can be grown in animals, they can be harvested without harming human beings. Note that this is entirely theoretical: using chimeras as a source of organ donations has not been put into practice.

[13]New Scientist and Press Association (2021) “Human cells grown in monkey embryos raise ethical concerns” NewScientist retrieved from on June 26, 2021

[14]Hotz, Robert Lee (2021) “Creation of First Human-Monkey Embryos Sparks Concern” The Wall Street Journal retrieved from on June 25, 2021

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